refactor and cleanup [skip ci]

submodules/Postbox/Sources/PreferencesTable.swift

@@ -0,0 +1,70 @@
+import Foundation
+
+enum PreferencesOperation {
+    case update(ValueBoxKey, PreferencesEntry?)
+}
+
+private struct CachedEntry {
+    let entry: PreferencesEntry?
+}
+
+final class PreferencesTable: Table {
+    private var cachedEntries: [ValueBoxKey: CachedEntry] = [:]
+    private var updatedEntryKeys = Set<ValueBoxKey>()
+    
+    static func tableSpec(_ id: Int32) -> ValueBoxTable {
+        return ValueBoxTable(id: id, keyType: .binary, compactValuesOnCreation: false)
+    }
+    
+    func enumerateEntries(_ f: (PreferencesEntry) -> Bool) {
+        self.valueBox.scan(self.table, values: { _, value in
+            if let object = PostboxDecoder(buffer: value).decodeRootObject() as? PreferencesEntry {
+                return f(object)
+            } else {
+                return true
+            }
+        })
+    }
+    
+    func get(key: ValueBoxKey) -> PreferencesEntry? {
+        if let cached = self.cachedEntries[key] {
+            return cached.entry
+        } else {
+            if let value = self.valueBox.get(self.table, key: key), let object = PostboxDecoder(buffer: value).decodeRootObject() as? PreferencesEntry {
+                self.cachedEntries[key] = CachedEntry(entry: object)
+                return object
+            } else {
+                self.cachedEntries[key] = CachedEntry(entry: nil)
+                return nil
+            }
+        }
+    }
+    
+    func set(key: ValueBoxKey, value: PreferencesEntry?, operations: inout [PreferencesOperation]) {
+        self.cachedEntries[key] = CachedEntry(entry: value)
+        updatedEntryKeys.insert(key)
+        operations.append(.update(key, value))
+    }
+    
+    override func clearMemoryCache() {
+        assert(self.updatedEntryKeys.isEmpty)
+    }
+    
+    override func beforeCommit() {
+        if !self.updatedEntryKeys.isEmpty {
+            for key in self.updatedEntryKeys {
+                if let value = self.cachedEntries[key]?.entry {
+                    let encoder = PostboxEncoder()
+                    encoder.encodeRootObject(value)
+                    withExtendedLifetime(encoder, {
+                        self.valueBox.set(self.table, key: key, value: encoder.readBufferNoCopy())
+                    })
+                } else {
+                    self.valueBox.remove(self.table, key: key, secure: false)
+                }
+            }
+            
+            self.updatedEntryKeys.removeAll()
+        }
+    }
+}